Radial piston engine with guide rollers

ABSTRACT

The invention concerns a technically optimized radial piston engine comprising a cam ring and a cylinder block arranged so as to rotate about an axis of rotation relative to the cam ring and having a plurality of cylinders oriented in the radial direction of the cylinder block. A piston capable of being radially displaced is located in each cylinder, resting on the cam ring via a roller. Said roller is mounted on the piston so as to rotate about an axis parallel to that of the cylinder block and rests axially, relative to its axis of rotation in the cylinder, against roller guides arranged on its surfaces. Said radial piston engine is characterized in that the roller guides are integrally mobile with the roller associated with them, in the piston stroke direction, and thereby driven by the roller both when the piston performs a loaded stroke and an idle stroke, without any contact occurring between the roller guides and the cam ring. The pistons are rotationally fixed by a torsional stop which is separate from the roller guide.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radial piston engine with rollerguides for axial guidance of the rollers, via which the pistons arebraced against the cam ring.

2. Discussion of the Background

From British Patent GB B 2238086 there is known a radial piston enginecorresponding to the preamble of claim 1, wherein the object was toreduce the manufacturing complexity previously associated with axialpositioning of the rollers and thus to lower the manufacturing andassembly costs. This object was supposedly achieved in that, in each ofthe spaces between the roller end faces and the cylindrical inside faceas the roller guide, there is disposed a wedge piece, whose crosssection viewed in piston displacement direction is a circular segment,and which positions the roller axially in the cylinder relative to thecam. ring. The wedge pieces disclosed in the cited patent can be dividedsubstantially into three different designs.

In a first design, each wedge piece has on the side facing the roller aplane surface which bears on the end face of the roller and on the sidefacing away from the roller a cylindrical surface which is in contactwith the inside face of the cylinder. In addition, this wedge piece isaccommodated in the space between roller, piston and cylindrical insideface, without being rigidly connected to any of these components. Byvirtue of the fact that the wedge piece is freely movable in pistondisplacement direction relative to the roller, the piston urges thewedge pieces toward the cam ring during a load stroke. In the process,the wedge pieces do not yet come into contact with the cams formed onthe cam ring. In the ensuing idle stroke of the piston, however, thewedge pieces strike the cams formed on the cam ring. This recurringstriking contact between the cams and the wedge pieces as well as thefriction occurring therebetween can lead to severe wear of the wedgepieces. A further disadvantage of this design is that the width of thecam ring must be at least sufficiently large that the cam ring inaddition to the roller also provides a contact face for the twolaterally disposed wedge pieces. Aside from large total weight of theradial piston engine, a broad cam ring results in high manufacturingcosts due to the greater manufacturing complexity associated withprecision machining of the cam ring.

In a second design, each of the two wedge pieces has on the side facingthe roller a driver-like projection, which extends toward the otherwedge piece in an opening provided in the piston between piston androller. Since in this case the wedge pieces are driven back into thecylinder by the roller during an idle stroke of the piston, strikingcontact between the wedge pieces and the cams basically cannot occur.Due to the high relative velocity between the roller and the driver-likeprojections of the wedge pieces in contact with the outsidecircumference of the roller, however, severe abrasion can take place onthe driver-like projections. With increasing abrasion of the driver-likeprojections, the space available for play of the wedge pieces in pistondisplacement direction could ultimately increase to the point thatstriking contact could occur between the wedge pieces and the cams. Afurther disadvantage of this design is that driver-like projections mustbe formed on the roller guides and recesses must be formed on thepiston, thus increasing the manufacturing complexity and thus themanufacturing costs.

In addition, the friction between the roller and the wedge pieces in thetwo foregoing designs occurs over the entire end face of the roller.This relatively large-area frictional contact necessitates precisionmachining of the friction faces of both components, once again resultingin high manufacturing costs.

At that time a further assumption was that, by virtue of the recurringcontact of the rollers with the cam ring, the rollers and thus therespective piston automatically assume a particular angular position inthe cylinder or relative to the cam ring, which is critical for reliableoperation of the radial piston engine. In certain cases, however, forexample during initial operation of the radial piston engine, whenhydraulic fluid is fed to the cylinders for the first time, it isconceivable that the pistons and thus the rollers may be inserted so farinto the respective piston that contact between roller and curved pathdoes not yet occur. To ensure the necessary angular position of thepiston in the cylinder in those cases, one of the two wedge pieces has,in a third design, on the side facing the cylindrical inside face, anelongated slot, into which a bolt, clamp or the like extending throughthe cylinder wall engages and in this way prevents turning of the pistonin the cylinder and thus of the roller relative to the cam ring. Thepresence of the slot leads to weakening of the wedge piece in question,however, and thus to shortening of the useful life of the wedge piece,which is subjected to severe stresses and strains during operation ofthe radial piston engine. In addition, sliding contact takes placebetween the wedge piece and the bolt or clamp, which appearsdisadvantageous as regards good roller guidance. Furthermore, such astructural feature means high manufacturing complexity.

BRIEF SUMMARY OF THE INVENTION

In view of the disadvantages encountered in conventional radial pistonengines, the object of the present invention is therefore to provide anoptimally engineered radial piston engine, which is characterized bygreater manufacturing simplicity and at the same time functionallyreliable operation.

This object is achieved by the inventive subject matter according to thefeatures of claim 1, which is characterized in particular in that theroller guides disposed on the front sides of the rollers are rigidlyconnected to the respective roller with respect to sliding in pistondisplacement direction.

Since the respective roller urges the roller guides in pistondisplacement direction, in other words both during the load stroke andduring the idle stroke, the roller guides can be dimensioned such thatthey do not project beyond the outside circumference of the respectiveroller, thus ensuring that striking contact does not take place betweenthe roller guides and the cam ring. This ultimately leads to longeruseful life of the roller guides and thus to functionally reliableoperation of the radial piston engine on the whole. In addition,material economies are achieved in the manufacture of the roller guides.

If the roller guides do not come into contact with the cam ring, thewidth of the cam ring can be further reduced to a width whichcorresponds at most to the width of the rollers. In this way, not onlyis the total weight of the radial piston engine lessened, but alsomanufacturing complexity and thus the manufacturing costs areconsiderably reduced with regard to precision machining of the curvedpaths of the cam ring.

By suitable structural measures, such as by formation of a cylindricalprojection on the roller guide, which projection is inserted in acorresponding recess on the front side of the roller, the relativevelocities at the friction faces of roller and roller guides and thusthe wear of the two components can also be reduced. Because of thereduced wear, the play developed between roller and roller guides iskept to a minimum, even after prolonged operating time. This contributesto functionally reliable and dependable operation of the radial pistonengine on the whole.

Further advantageous features of the inventive radial piston engine aresubject matter of the dependent claims.

The roller and roller guides can be rigidly connected with respect tosliding in displacement direction by simple manufacturing techniques.For example, the roller guides can be provided on the side facing theend face of the roller with a cylindrical projection, which isinsertable into a central cylindrical recess formed on the end face ofthe roller. Likewise, it would naturally also be conceivable for theroller guides to be provided on the side facing the front side of theroller with a recess into which a projection formed on the front side ofthe roller is insertable. Of course, the opening and the projectionengaged therewith could also have conical shape. If the diameter of theopenings and projections are dimensioned such that they are smallcompared with the outside diameter of the roller, or in other words suchthat the projections and the openings are concentrated on a centralregion around the axis of rotation of the roller, and if the projectionsare engaged with the respective openings in such a way that play ispresent between the annular face of the roller around the opening and ofthe face around the projection of the roller guide, the circumferentialvelocities present at the outside circumference of the projection and atthe inside circumferential wall of the opening during operation of theradial piston engine are reduced, as is therefore the relative velocitybetween roller and roller guides. Moreover, since no friction occurs atthe two spaced-apart faces of roller and roller guide, reduction offrictional abrasion of both components is achieved.

The surfaces of the roller guides in contact with the cylindrical insideface preferably have cylindrical shape for simplicity, thus achievingoptimal guidance of the piston-roller system in the cylinder. Since theroller is normally not subjected to compressive loads in axialdirection, it would also be conceivable, however, to give the surface ofthe roller guide bearing on the cylindrical inside face rotationallysymmetric shape or to construct it as a spherical segment relative tothe axis of rotation of the roller. In this case, rigid connectionbetween roller guide and roller would even be possible both in pistondisplacement direction and in the direction of rotation of the roller.This would have the advantage that, during operation of the radialpiston engine, friction between roller and roller guides would no longertake place and the friction occurring between roller guide andcylindrical inside face would be considerably reduced.

Heretofore it has been assumed that the roller is constantly in contactwith the curved paths of the cam ring, whereby the angular position ofthe piston in the cylinder and accordingly the orientation of the rollerrelative to the curved path is automatically predetermined. As alreadyexplained in the introduction, however, it is possible for the contactbetween roller and cam ring to be separated. In this case it is possibleaccording to the present invention to prevent turning of the piston inthe cylinder by means of an antirotation device disposed separately fromthe roller guide and thus to maintain a particular orientation of theroller relative to the cam ring.

For this purpose, the piston can be provided on the end portion facingaway from the roller with a flattened part oriented perpendicularrelative to the axis of rotation of the cylinder block, which flattenedpart bears on a corresponding contact face of the antirotation device,thus unambiguously predetermining the angular position of the piston inthe cylinder and of the roller relative to the curved path. Anothereffective expedient has proved to be providing the cylinder with atleast two cylinder portions of different inside diameters and the pistonaccordingly with at least two piston portions of different diametersmatching the corresponding cylinder diameters. In this case, theantirotation device is provided in the cylinder portion with the smallerinside diameter and the flattened part is provided accordingly on thepiston portion with the smaller diameter. By this expedient, on the onehand a large face for admission of pressure is retained on the pistonand on the other hand only little material is removed from the piston inorder to form the flattened part. The additional antirotation devicecreates better guidance of the piston in the cylinder compared with theconventional antirotation device mentioned in the introduction, sinceaccording to the present invention large-area sliding contact takesplace between piston and antirotation device.

The antirotation device preferably has a cross section which, viewed inpiston displacement direction, is a circular segment, with an arccorresponding to the cylindrical inside face and a chord correspondingto the flattened part.

Since the cylinder block in any case is normally provided with axialinlet ports, through which the hydraulic fluid enters the respectivecylinder spaces, the manufacturing complexity with regard to fixing theantirotation device in the cylinder can be reduced in that theantirotation device is fixed in the cylinder by means of a pin, which isinserted through the inlet port into a blind hole in the cylinder blockaligned with the inlet port.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

Further features and advantageous embodiments of the present inventionwill become clear from the description hereinafter of preferredembodiments with reference to the drawing, wherein

FIG. 1 shows a longitudinal section of a preferred embodiment of theinventive radial piston engine;

FIG. 2 shows a cross section through the cylinder block in FIG. 1 alongline II—II;

FIG. 3a shows a section on larger scale through the cylinder block inFIG. 2 along line III—III;

FIG. 3b shows a perspective view of the piston;

FIG. 4 shows a section through the cylinder block along line IV—IV inFIG. 1;

FIG. 5 shows a perspective view of the roller guide;

FIG. 6 shows a section through the cylinder block along line VI—VI inFIG. 1;

FIG. 7 shows a perspective view of the antirotation device;

FIGS. 8a and 8 b show modifications of the roller guide in FIG. 5;

FIGS. 9a and 9 b show modifications of the connection between rollerguide and roller in FIG. 5; and

FIGS. 10a and 10 b show modifications of the cylinder block in FIG. 3a.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 to 6 there will be described a preferredembodiment of the inventive radial piston engine. Radial piston engine 2comprises, as illustrated in FIG. 1, substantially two housing parts 4and 6 as well as a cam ring 8 disposed between the two housing parts 4and 6. The two housing parts 4 and 6 and cam ring 8 are coaxiallyconnected to one another in fluid-tight manner by means of bolts 10. Onthe inside face of cam ring 8 there is formed a curved path 12 with aplurality of cams 14, as can be seen in particular in FIG. 2.

Inside cam ring 8 there is disposed a cylinder block 18 which can rotatearound a longitudinal axis of rotation 16. As is evident in FIGS. 1 and2, cylinder block 18 is provided with a central opening 20 having aninternal toothing. In this opening 20 there is accommodated in axialsliding relationship an end portion 22 of a driven shaft 24, which isequipped with an external toothing corresponding to the internaltoothing of opening 20. By means of a bearing assembly 30, driven shaft24 is mounted to rotate relative to the two housing parts 4 and 6 and tocam ring 8. Bearing assembly 30 comprises two tapered roller bearings 32and 34, which are mounted in housing part 4 and can transmit large axialand radial forces. The other end portion 26 of driven shaft 24 projectsout of housing part 4 and is provided with a shaft flange 28 forfastening to a drive element (not shown) of a device to be driven, suchas a gear of a loader.

In cylinder block 18 there is also formed a plurality of cylinders 36directed radially outward in a star pattern relative to axis of rotation16, which cylinders have cylinder axis 37 perpendicular relative to axisof rotation 16. As is evident in the enlarged illustration in FIG. 3a,cylinder 36 has a cylinder portion 38 of large inside diameter disposedradially outward relative to axis of rotation 16, as well as a cylinderportion 40 with small inside diameter disposed radially inward. Cylinderportion 38 is open at the substantially cylindrical outsidecircumferential face 42 of cylinder block 18. Furthermore, there isformed in cylinder block 18 an inlet port 43, which is parallel tolongitudinal axis of rotation 16 and opens into cylinder portion 40, andvia which hydraulic fluid is supplied and removed during operation ofradial piston engine 2.

In cylinder 36 there is accommodated a piston 44 which, as shown in FIG.3b, has piston portions 46 and 48. Piston portion 46 has a diametercorresponding substantially to the inside diameter of cylinder portion38. Piston portion 48 has on its outside circumference two flattenedparts 48 a and 48 b which, as is evident in FIG. 6, are orientedperpendicular to axis of rotation 16. The diameter of the outsidecircumference of piston portion 48 corresponds to the inside diameter ofcylinder portion 40. Flattened part 48 b defines a contact face, whichbears on a correspondingly provided contact face 50 b of an antirotationdevice 50, to be described in more detail hereinafter. Flattened portion48 a faces inlet port 43.

When cylinder 36 is supplied with hydraulic fluid via inlet ports 43during operation of radial piston engine 2, pistons 44 are pressurizedselectively to the effect that they execute a displacement movementtoward cam ring 8. In the process they are each braced via acorresponding roller 54 against curved path 12 formed on cam ring 8. Asshown in FIG. 1, axial width B of the cam ring in this embodiment ofradial piston engine 2 corresponds substantially to the axial length ofrollers 54. On the end portion of each piston portion 46 facing cam ring8 there is formed a bearing 56, in which there is accommodated therespective roller 54, mounted to rotate relative to piston 44 around anaxis of rotation 58.

As shown in FIGS. 1, 3 a, 4 and 5, a roller guide 60 is disposed at eachof the two front sides 54 a and 54 b of roller 54, whereby the axialposition of roller 54 in cylinder 36 and thus relative to piston 44 andcurved path 12 is predetermined. Roller guides 60 are each disposed in aspace formed between end faces 54 a and 54 b of roller 54, piston 44 andthe cylindrical inside face of cylinder 36. FIG. 5 shows a perspectiveview of roller guide 60 which, viewed in piston displacement direction,has a cross section substantially in the form of a circular segment. Onthe chord side facing front side 54 a or 54 b of roller 54, each rollerguide 60 has a cylindrical projection 62 which is axial relative to axisof rotation 58 and which is engaged with a corresponding central recess54 c or 54 d on front sides 54 a and 54 b of roller 54. Cylindrical arcside 63 of each roller guide 60 bears on the cylindrical inside face ofcylinder 36. The length of axial projection 62 is somewhat greater thanthe depth of recess 54 c and 54 d, and so play exists between the faceof roller guide 60 around central projection 62 and each annular face onfront sides 54 a and 54 b of roller 54 around central recess 54 c and 54d.

By virtue of the type of connection of roller guides 60 with roller 54described hereinabove, roller guides 60 are driven in pistondisplacement direction by respective roller 54 during operation ofradial piston engine 2, or in other words during a displacement movementof the piston. Since, as described hereinabove, the width of the camring corresponds to the length of the rollers, striking contact betweenthe roller guides and the cam ring does not occur during operation ofthe radial piston engine according to this embodiment, regardless ofwhether the roller guides project beyond the roller in pistondisplacement direction. In addition, the wear of both components due tothe relative velocity that occurs between roller guides and rollerduring operation of the radial piston engine can be reducedconsiderably, since the friction between the two components occurs in arange in which the relative velocity is quite low.

As is evident in FIG. 6 and has already been mentioned hereinabove,there is provided at the cylindrical inside face of cylinder portion 40opposite inlet port 52 a so-called antirotation device 50, which has thefunction of preventing turning of piston 44 in cylinder 38 around acylinder axis 37. The critical factor here is that a particular angularposition of piston 44 relative to cylinder axis 37 and thus of roller 54relative to curved path 12 is maintained. Antirotation device 50 isfastened to cylinder block 18 by means of a pin 76, such as a taperedpin, straight pin or grooved pin in the manner shown in FIG. 3a or FIG.6. FIG. 7 shows a perspective view of antirotation device 50 which,viewed in piston displacement direction, has in common with roller guide60 a cross section in the form of a circular arc, wherein cylindricalarc side 50 a bears on the cylindrical inside face of cylinder portion40 and chord side 50 b bears on flattened part 48 b formed on pistonportion 48 of piston 44. In contrast to roller guide 60, which in thisembodiment of the radial piston engine is provided with a projection 62,there is formed in antirotation device 50 a cylindrical opening 78, inwhich there is seated the part of pin 76 which projects out of blindhole 84, disposed in cylinder block 18 in such a way as to be alignedwith inlet port 43.

Reference symbol 66 denotes a fluid-control unit, by means of which, viainlet ports 43, hydraulic fluid is supplied to the respective cylinderspaces or removed from the respective cylinder spaces during operationof radial piston engine 2. Fluid-control unit 66 is disposed influid-tight relationship in housing part 6 such as to rotate therewith.In order to be able to distribute hydraulic fluid to the respectivecylinder spaces, fluid-control unit 66 is provided with two separatecircumferential grooves 68 and 70, which are in communication with fluidchannels 72 and 74 respectively. During operation of radial pistonengine 2, fluid channels 72 and 74 come alternately into communicationwith axial inlet ports 43, which are formed in cylinder block 18 andeach of which communicates with one of the cylinder spaces.

During operation of radial piston engine 2, pistons 44 are actuated bymeans of hydraulic fluid via fluid channels 68, 70, 72 and 74, inletports 43 and the cylinder spaces in such a way that they are urgedradially outward relative to axis of rotation 16. In the process theyare braced via the respective roller 54 against curved path 12 of camring 8, whereby cylinder block 18 is ultimately caused to perform arotary movement around axis of rotation 16. The direction of rotation isselected by the mode of actuation. Because of the positive connection ofdriven shaft 24 to cylinder block 18, a torque is transmitted to drivenshaft 24. This shaft is braced via tapered roller bearings 32 and 34 ofbearing assembly 30. A drive element such as a gear of a loader (notillustrated in more detail here), which is connected via flange portion28 to drive shaft 24, therefore receives a torque.

FIGS. 8a and 8 b show modifications of the roller guides described inconnection with the foregoing embodiment of the inventive radial pistonengine.

Roller guide 90 illustrated in FIG. 8a differs from roller guide 60shown in FIG. 5 in that, at the upper outside face facing cam ring 8, itis rounded in a manner corresponding to the outside circumference ofroller 54 and is designed to ensure that it does not project beyond theoutside circumference of the roller in piston displacement direction.Since roller guide 90 in this case does not project beyond the outsidecircumference of roller 54, and since in addition it is rigidlyconnected to roller 54 with respect to sliding in piston displacementdirection, roller guide 90 could also be used—of course, only togetherwith inventive roller 54—for a conventional radial piston engine with acam ring, in which the cam ring has a width which is greater than thelength of roller 54.

Whereas surfaces 63 of roller guides 60 in contact with the cylindricalinside face were of cylindrical structure hereinabove for the sake ofsimplicity, roller guide 92 shown in FIG. 8b is provided on the sidefacing the cylinder face with a surface 93 which is rotationallysymmetric or has the form of a spherical segment relative to axis ofrotation 58 of roller 54. Since the roller and thus also the rollerguides normally do not experience particularly large axial loads duringoperation of the radial piston engine, the service life of the rollerguides should not be shortened by giving the structure of the rollerguides the form of a spherical segment. In order constantly to achievereliable axial positioning of the rollers in this case, however, it isnecessary that the extent to which the pistons are displaced duringoperation of the radial piston engine is sufficiently limited that axisof rotation 58 of each roller 54 is still disposed inside the cylindereven at maximum piston displacement. This restriction is not necessaryin the roller guides mentioned hereinabove, however, because they are incontact over a large area.

In the special case shown in FIG. 8b, roller guides 92 could beconnected positively and nonpositively to roller 54 not only in pistondisplacement direction but also in the direction of rotation of roller54, so that friction no longer develops between roller and roller guide.Because of the small, substantially only linear contact of roller guide92 on the cylindrical inside face, the friction occurring between rollerguide 92 and cylindrical inside face would also be considerably reduced.Since roller guides 90 and roller 54 then can no longer turn relative toone another, the positive and/or nonpositive connection between rollerguide and roller could also be achieved in any other manner. It wouldeven be conceivable to construct the roller and the roller guides in onepiece, or in other words to provide the roller guides on the roller.

FIGS. 9a and 9 b show further options for connecting the roller guidesto the roller.

Whereas in the preferred practical example of inventive radial pistonengine 2 described hereinabove there were formed on each roller guide aprojection 62 and on the roller corresponding recesses 54 c and 54 d,roller guide 94 according to FIG. 9a is provided with a recess 95 androller 96 with a corresponding projection 97. In this example also, playis present between the oppositely disposed faces on roller guide androller around the recess or around the projection, whereby the frictiondeveloped between these components occurs in a range in which smallrelative velocities exist between roller and roller guides. However, thepresent invention is not limited merely to this arrangement; it wouldnaturally also be conceivable for the roller guides to be directly incontact with the roller in the conventional sense, or in other wordswithout play.

Roller guide 98 in FIG. 9b is characterized by a conical projection 99,which is engaged with a corresponding central recess 101 of conicalshape on roller 100. In this case the roller guide is engaged with theroller without play but, as is also the case in the foregoing examples,the area of contact between roller 100 and roller guides 98 is relocatedinto a central region relative to axis of rotation 58.

In the preferred embodiment there is provided an antirotation device 50,which prevents turning of piston 44 in cylinder 36 and thus turning ofroller 54 relative to curved path 12. Since the rollers are normallyconstantly in contact with the curved path, however, whereby the angularposition of the roller and thus of the piston is automaticallydetermined, it is not absolutely necessary to provide an antirotationdevice. This case is shown in FIG. 10a. Here the structure of thecylinder and piston is simplified substantially, since specialmanufacturing steps do not have to be performed either for piston 102 orfor the cylinder block.

It is also possible by another relatively simple structural modificationto the piston and cylinder block, however, as shown for example in FIG.10b, to provide an antirotation device 106 for piston 104 without havingto form the piston and cylinder as stepped structures.

At this juncture it should be pointed out that all features describedhereinabove, especially in connection with the geometry of the rollerguide, the connection between roller guides and rollers, and also theantirotation device for the pistons, can be combined with one another tothe extent technically possible.

The present invention therefore creates a technically optimized radialpiston engine with a cam ring and a cylinder block, which is disposed torotate relative to the cam ring around an axis of rotation and which hasa plurality of cylinders aligned in the radial direction of the cylinderblock. In each cylinder there is disposed a piston which can bedisplaced in radial direction, and which is braced via a roller againstthe cam ring. The roller is mounted in a bearing provided on the pistonsuch that it can rotate around an axis of rotation parallel to the axisof rotation of the cylinder block while being braced axially in thecylinder relative to its axis of rotation via roller guides disposed atits front sides. The inventive radial piston engine is characterized inparticular in that the roller guides are rigidly connected with therespective roller with respect to sliding in piston displacementdirection and accordingly are urged in piston displacement direction bythe respective roller both during a load stroke and during an idlestroke of the piston, whereby the roller guides do not come into contactwith the cam ring.

We claim:
 1. A radial piston engine (2) with a cam ring (8), a cylinderblock (18) disposed to rotate relative to the cam ring (8) around anaxis of rotation (16), the said block having a plurality of cylinders(36) aligned in radial direction of the cylinder block (18), in each ofwhich cylinders there is accommodated a slidable piston (44), which isbraced via a roller (54, 96, 100) against the cam ring, wherein theroller is mounted on the piston to rotate around an axis of rotation(58) parallel to the axis of rotation (16) of the cylinder block (18)and, relative to its axis of rotation (58), is braced axially in thecylinder (36) via roller guides (60, 90, 92, 94, 98) disposed at its endfaces, characterized in that the roller guides (60, 90, 92, 94, 98) arerigidly connected to the respective roller (54, 96, 100) with respect tosliding in piston displacement direction.
 2. A radial piston engineaccording to claim 1, characterized in that the roller guides (60, 90,92, 98) are provided on the side facing the end face of the roller (54,100) with a projection (62, 99), which is insertable into a recess (54c, 54 d, 101) formed on the end face of the roller.
 3. A radial pistonengine according to claim 1, characterized in that the roller guides(96) are provided on the side facing the end face of the roller (96)with a recess (95), into which a projection (97) formed on the end faceof the roller is insertable.
 4. A radial piston engine according to oneof claims 1 to 3, characterized in that the roller guides (60, 90, 94,98) have on the side facing away from the end face of the roller acylindrical surface corresponding to the cylindrical inside surface. 5.A radial piston engine according to one of claims 1 to 3, characterizedin that the roller guides (92) have on the side facing away from the endface of the roller a surface which is rotationally symmetric or has theform of a spherical segment relative to the axis of rotation (58) of theroller.
 6. A radial piston engine according to claim 5, characterized inthat the roller guides (92) are connected with the roller to rotatetherewith in the direction of rotation of the roller.
 7. A radial pistonengine (2), especially according to one of the preceding claims, with acam ring (8), a cylinder block (18) disposed to rotate relative to thecam ring around an axis of rotation (16), the said block having aplurality of cylinders (36) aligned in radial direction of the cylinderblock, in each of which cylinders there is accommodated a slidablepiston (44), which is braced via a roller (54, 96, 100) against the camring, wherein the roller is mounted on the piston to rotate around anaxis of rotation (58) parallel to the axis of rotation (16) of thecylinder block (18) and, relative to its axis of rotation (58), isbraced axially in the cylinder via roller guides (60, 90, 92, 94, 98)disposed at its end faces, characterized by an antirotation device (50),disposed separately from the roller guides, to prevent turning of thepiston in the cylinder.
 8. A radial piston engine according to claim 7,characterized in that the piston is provided on the end portion facingaway from the roller with a flattened part, which bears on acorresponding contact face of the antirotation device.
 9. A radialpiston engine according to claim 8, characterized in that the cylinderis provided with at least two cylinder portions (38, 40) of differentdiameters and the piston is provided accordingly with at least twopiston portions (46, 48) of different diameters matching thecorresponding cylinder diameters, the antirotation device being providedin the cylinder portion (40) with the smaller inside diameter and theflattened part being provided on the piston portion (48) with thesmaller diameter.
 10. A radial piston engine according to claim 9,characterized in that the antirotation device has a cross section which,viewed in piston displacement direction, is a circular segment, with anarc corresponding to the cylindrical inside face and a chordcorresponding to the flattened part.
 11. A radial piston engineaccording to one of claims 7 to 10, characterized in that theantirotation device is fixed to the cylindrical inside face of thecylinder portion (40) with the smaller diameter by means of a pin (76),which is inserted via an inlet port (43) for supply and removal ofhydraulic fluid in the cylinder space, the pin (76) being fastened in anopening (84) in the cylinder block (18) aligned with the inlet port(43).